1. Field of the Invention
The present invention relates to a motor, and in particularly to a motor having a stator and a rotor mounted on the stator so as to be rotatable about a rotation axis. The present invention also relates to a printer having such a motor, and a disk drive system having such a motor.
2. Summary of the Prior Art
It is well known to provide a motor with a stator and rotor, and to drive the rotor about a rotation axis using suitable drive means. That drive means may, for example, be a coil mounted on the stator which receives a current which interacts with the magnetic field of a permanent magnet on the rotor to generate a force to rotate the rotor.
In such a motor, it is important that radial movement of the axis of rotation of the rotor is prevented, or at least restrained, and therefore it is known to provide a magnetic thrust bearing which applies a thrust force in a direction radial of the rotor axis between the rotor and the stator. Such a magnetic thrust bearing may comprise a first permanent magnet on the rotor and a second permanent magnet on the stator, with the first and second permanent magnets being concentrically arranged around the rotation axis, and having a radial gap therebetween. By suitable arrangement of the polarity of the first and second permanent magnets, a thrust force may be generated therebetween which stabilizes the rotation of the rotor. A motor incorporating such a magnetic thrust bearing is disclosed in, for example, JP-A-4-150753 (corresponding to U.S. patent application No. 07/629462, now U.S. Pat. No. 5,325,006). Other examples of magnetic thrust bearings are disclosed in JP-A-61-201916, JP-A-62-85216 and JP-A-63-88314.
Motors of the type discussed above are used in printers and disk drives. In a laser printer, the laser beam is caused to scan the surface on which printing is to occur. That scanning is achieved by directing the beam onto a rotating polygonal mirror, so the speed of scanning is determined by the speed of rotation of the polygonal mirror. A motor described above may then be used to rotate the polygonal mirror. Similarly, in a disk drive, a disc is caused to rotate and that rotation may be achieved by a motor described above. To achieve high density of data recordal on the disk, it is necessary to use a high speed of rotation.